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Feb, 14, 195 J. G. CALTON 2,734,794

PROCESS FOR WET-DRAWING POLYETHYLENE TEREPHTHALATEZ Filed July 12. 1951 FROM FEED L: :1: TO W/ND UP INVENTOR. Joseph Gordon Ca/fon MZM A TTORNE f.

United States Patent PROCESS FOR WET-DRAWING POLYETHYLENE TEREPHTHALATE Joseph Gordon Calton, Buffalo, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application July 12, 1951, Serial No. 236,399

5 Claims. (CI. 18-54) This invention relates to a process for preparing resil ient polyethylene terephthalate fibers and is particularly concerned with a process for producing polyethylene terephthalate fibers and yarn possessing desirable characteristics of fine wool.

Considerable research effort has been directed toward discovering or developing a satisfactory substitute for natural wool. A particular aim has been to produce a synthetic fiber possessing the desirable characteristics of fine wool, such as that used in suits and outer garments, in addition to launderability and freedom from attack by moths. Various synthetic fibers have been subjected to many different processes, both mechanical and chemical, in an effort to so modify their properties that they could be classified as wool-like material. The prior art discusses at length the use of stable fiber-making equipment and crimpers, as well as various chemical and heattreating methods, for treating synthetic fibers in order to secure characteristics normally associated with natural wool. In no instance, however, have these synthetic materials been satisfactory substitutes for W001. Other than in superficial appearance, they cannot properly be classified as wool-like. A great new field of use would be open to a synthetic fiber which could be woven into fabrics having the hand, resilience, wrinkle-resistance, fullness, warmth, and other such properties normally associated with fine woolen fabrics.

It has now been found that desirable wool-like characteristics can be built into fibers and yarns prepared from the new synthetic linear polyesters described in United States Patent No. 2,465,319 to Whinfield and Dickson. These are highly polymeric linear esters of terephthalic acid which are high melting, difficultly soluble, substantially colorless materials suitable for forming into filaments. The filaments can be extended by drawing into strong flexible fibers showing, by characteristic X-ray patterns, molecular orientation along the fiber axes. This has been accomplished by drawing the fibers at elevated temperatures to a high draw ratio, i. e., to several times the original fiber length.

It is an object of this invention to provide a process for producing polyethylene terephthalate fibers having the resilience characteristics of the better grades of wool. A further object is to provide a process for preparing uniform, drawn polyethylene terephthalate fibers of woollike properties, which fibers will not be subject to additional cold drawing during subsequent normal processing. Other objects will become apparent from the following description of the invention and the appended claims.

These objects are accomplished by drawing polyethylene terephthalate fibers which have a birefringence in the range of 0.004 to 0.11 to 90% to 100% of the maximum draw ratio obtainable at temperatures in the range of 35 to 50 C. while the fibers are wet with a hydroxylated non-solvent, preferably water or a dilute aqueous solution.

With wet fibers having the specified birefringence the 2,734,794 Patented Feb. 14, 1956 maximum draw ratio obtainable at 35 to 50 C. will be within the range of about 2.7 to 4.1 times. The resilient properties associated with fine wools are developed in the drawn polyethylene terephthalate fibers by subsequently relaxing them in a free-to-shrink condition at temperatures in the range of to 200 C.

In the accompanying drawing the single figure illustrates schematically a front elevation of a form of apparatus for drawing yarn in accordance with the above process. I

The above process conditions are critical, as will be set forth in greater detail subsequently. However, it may be emphasized at this point that the desired properties will not be obtained unless the fibers are subjected to at least 90% of the maximum draw and the maximum draw ratio is from about 2.7 to 4.1 times'the original length of the fibers. It had previously been thought that polyethylene terephthalate fibers must be drawn at temperatures of 60 C. and above in order to avoid excessive breaking of the filaments during the process. However, the maximum draw at 60 ,C. greatly exceeds 4'times. When an attempt is made to use partial draw ratios as low as 3 to 4 times at temperatures of 60 C. or above, even in the presence of water, the process is extremely difficult to control and the product is notiuniform. Such partial drawing at temperatures of 60 C. and above gives rise to non-uniformities of dye receptivity, nonuniformi'ties of denier, and the product undergoes further cold-draw at relative low tension levels during subsequent mill-processing, particularly in staple spinning operations.

Certain conditions referred to above or elsewhere in the specification require explanation. {The fiber-forming material is principally polyethylene"terephthalate but the inclusion therein of up to 10 mol per cent of modifying material is intended 'wheneverthe expression polyethylene terephthalate material is used. Polyethylene terephthalate, itself, is a poly-condensation product of ethylene glycol and terephthalic acid or an ester-forming derivative thereof. During the preparation of this polyester, minor amounts of a modifying material may be added, for example, another glycol and/or'another dicarboxylic acid. Thus a'suitable funicular structure comprised essentially of polyethylene terephthalate may-have included in the polymer molecule up to 10 mol per cent of another glycol such asdieth ylene glycol,'tetramethylene glycol or hexamethylene glycol. Or again, the molecule may contain up to 10 mol per cent of another acid. As suitable examples of modifying acids, there may be mentioned hexahydroterephthalic acid, bibenzoic acid, adipic acid,'sebacic acid, azelaic acid, the naphthalic acids, 2.5-dimethylterephthalic acid and bis-p-carboxyphenoxyethane.

These modifiers may be added as one of the initial reactants during the polymerization process, but the modifying materials may also be polymerized-separately and then melt-blended with the polyethylene terephthalate. In either case, the total amount of modifier in the final polymeric material should not exceed 10 mol per cent. The polyesters are suitably prepared as described in U. S. Patent 2,465,319.

The ethylene terephthalate polymer preferably has an intrinsic viscosity of at least 0.3. Those polymers :having lower intrinsic viscosities are essentially non-fiber forming. The expression intrinsic viscosity" is used herein as a measure of the degree of polymerization of the polyester and may be defined as limit s r as C approaches 0 and 5.0% for each determination.

sharp creasing.

chloroethane, divided by the viscosity of the phenol-tetrachloroethane mixture, per 'se, measuredin. the same units at the same temperature, and C is the concentration in grams of polyester per 100 cc. of solution. The yarns and fibers prepared in accordance with the process of this invention possess a property of wool which is mostdifficult to duplicate, namely, resilience. This property is not easy to measure quantitatively, but may be defined to a considerable extent by three important parameters: Initial'tensile modulus, tensile recovery, and compliance ratio.

The initial tensile modulus (represented by the symbol M1 is defined as the slope of the first reasonably straight portion of a stress-strain curve of the funicular structure obtained by plotting tension on a vertical axis vs. elongation on a horizontal axis as the structure is being'elongatcd at the rate of per minute under standard conditions of temperature (21 C.) and humidity (60% RH). In almost every instance, this first reasonably straight portion is also'the steepest slope to be found on the curve. The values as used herein are in units of kilograms per square millimeter per 100% elongation.

The initial tensile modulus, Mi is a measure of resistance to stretching and bending. The effects of the filament modulus are felt in a fabric chiefly when the fabric is folded or crushed in the hand or otherwise handled. If the modulus is too low, the fabric is rubbery" or limp"; with too high a modulus in the fibers, the fabric is wiry or boardy. When the modulus is in the proper range, a soft fabric results. Attempts have been made to counteract the effects of a modulus lying outside the wool range by a suitable adjustment of filament diameter. In each instance, this straying away from the usual diameters of wool filaments has resulted 'in deleterious effects on properties such as liveliness and recovery from wrinkling. Since the filament properties which are almost entirely responsible for fabric resistance to bending are .(1) the initial modulus and (2) the diameter, and since the range of suitable diameters seems to be confined to those typical of wool, it follows that a wool-like'handlc will be obtained in the fabric when fibers having an initial modulus in the wool range are used.

The tensile recovery (TR) is defined as the extent to which the yarn recovers its original length after being stretched, a stress-strain curve being used to determine tensile recovery under the testing conditions. The test consists in extending the funicular structure at a constant rate of elongation of 10% per minute. A specimen is held at the maximum elongation desired for 30 seconds, e. g., by the use ofa time switch, and is then allowed to retract at the same rate at which it was extended. The same specimen is extended approximately 1.0, 3.0 The extension during elongation and the recovery during retraction are measured along the elongation axis. The tensile recovery is then the ratio of the extent to which the yarn retracts to the extent to which it was elongated. This test is run under standard conditions at 60% RH and 21 C.

It is well known that resistance to wrinkling and mussing and rapid recovery from unavoidable wrinkles are highly desirable traits in apparel fabrics. The tensile recovery correlates in a high degree with these properties. The tensile recoveryfroma 1% elongation correlates with fabric recovery from mild wrinkling, and, as might be expected; the tensilerecoveryrfrom higher elongations correlates with recovery from rnore'severe wrinkling and In this instance, the words, resistance to may be used alternatively to recovery from?" since resistance to a crease or wrinkle really involves a very rapid and complete recovery from a crease or-wrinkle when the deforming force is removed. The rapid recovery is a characteristic of the polyethylene terephthalate materials of this invention.

.The .compliance ratio (OR) isessociated with the shape of a stress strain curvean'd'is atmeasure 'ofithe rate of change of compliance with elongation. Compliance is defined' as elongation divided by tension-in kg./mm. Hookean systems, those for which the stressstrain curve is a straight line, exhibit equal compliance at all elongations, and for these the change of compliance with elongation is 0. On the other hand, one of the most important properties of wool is its change toward higher complianceas it is progressively deformed. Itis this property which enables wool to feel simultaneously crisp and soft. This property is measured by determining the average rate at which compliance changes in the range 5 to 10% elongation and is computed by the'following formula:

The stress-strain curve of wool has two distinctly different regions, consisting of (1) an initial portion in which the resistance to deformation is relatively great, and (2) a later portion in which the resistance decreases regularly and to a high degree. It is for this reason'that a'wool fabric which is crisp and firm to the touch will fecl'soft and compliant when severely crushed in the hand. Among the natural fibers this dualistic behavior is found only in wool and other animal hairs (not in silk, cotton, etc.), and this is one of the most attractive and valuable characteristics of wool.

In applying the above methods for evaluating wool-like resilience, it has been found that the better grades of wool for outer garment uses havev'alues for these three parameters in the following ranges:

Mi=ll0 to 550 kgjmm. CR=0.05 to 0.17 TR=55% or more from extensions of 3% In accordance with the process of the present invention synthetic yarns or fibers are produced which have woollike resilience within the above limits. Furthermore, the resulting synthetic fibers have these desirable resilience characteristicsthroughout by virtue of uniform treatment therealong during'formation and subsequent processing.

The following examples are illustrative of this invention and are not to be construed as limitative. The bircfringence (or double refraction) of the filaments was measured by the retardation technique described in Modern Textile Microscopy by J. M. Preston (London, 1933) page 270, using a petrographic microscope (Baus'ch & Lomb, Model LB) together with a 'Bausch & Lomb styleB cap analyzer compensator.

EXAMPLE 1 Polyethylene terephthalate in chip form having an intrinsic viscosity of 0.60 was melted on a heated grid and metered through a suitable filter pack. It was then extruded through a spinneret having fiftythree-holes into room temperature air. The extruded filaments were cooled and solidified by passage through the air and subjected after solidification to a means for winding them into a suitable package at the rate of 1206 yards per minute. The filaments of this '460 denier yarn exhibited a birefringence of 0.0060. v 7

Several ends of yarn'prepared in this fashion were combined vto'forrn a tow which was'rnetered by a series of four rolls, each comprising at a surface speed of 52' yards per minute, into an aqueous bath heated to a temperature of 40 C. and containing 1.4% by weight of Avitcx-R, a fatty alcohol sulfate textile finishing agent. The tow was withdrawn from the bath by means of a series of length. From the draw rolls, the tow was passed-through a smiling box type crimper, operating to apply 10-12 criihps per inch. The tow was then dropped in a free-toshrink condition onto an endless belt which carried it through an air oven heated to 155-165 C., the period of travel through-the oven being two minutes. The resulting relaxed product, before or after cutting into staple, possessed the properties shown in the following table:

Table I Tenacity in grams/denier 3.3 Elongation at break percent 40 Initial modulus in l g./mm. 317 Compliance ratio 0.067 Tensile recovery from 3% elongations percent 55 EXAMPLE 2 v ',Polyethylene terephthalate having an intrinsic viscosity of 0.61 was spun into a yarn in the manner described in Example 1, at a speed of 978 yards per minute. The filaments of this yarn exhibited a birefringence of 0.0058. This yarn was processed into three denier-per-filament staple essentially as described in Example 1. The yarn was drawn about 3.85 times at 40 C., using water to Wet the yarn instead of the aqueous finish bath of Example 1. Before cutting to staple the tow was relaxed in a boiling water shower and dried. These staple fibers had the properties shown in Table II.

Table II Tenacity in grams/denier 2.85 Elongation at break percent 62 Initial modulus in kg./mm. 249 Compliance ratio 0.103 Tensile recovery from 3% elongations percent 60 EXAMPLE 3 A copolyester prepared from ethylene glycol and a mixture of terephthalic acid and sebacic acid, containing 95% by weight of terephthalic acid and having an intrinsic viscosity of 0.58, Was spun into yarn in the manner of Example 1 at a speed of 978 yards per minute. The filaments of this yarn exhibited a birefringence of 0.0048. This yarn was processed into three denier-perfilament staple in the manner described in Example 1. The properties of the final staple product are listed in Table III.

Table III Tenacity in grams/ denier 2.6 Elongation at break percent 51 Initial modulus in kg./mm. 280 Compliance ratio 0.089 Tensile recovery from 3% elongations percent 55 EXAMPLE 4 Table IV 1.5 denier 4.5 denier Tenacity 3. 5 3. 5 Elongation 45 40 Initial modulus- 390 305 Compliance ratio 0. 075 0. 068 Tensile recovery from 3% elongat1ons percent. 60 55 The'filaments from polyethylene terephthalate yarn exhibiting a birefringence outside the range of 0.004 to 0.011 will not draw satisfactorily according to the process of this invention. When the birefringence is less than 0.004, one encounters excessive breakage and undrawn filaments in attempting to draw at temperatures below 60 C. On the other hand, when the filaments exhibit a birefringence above 0.011, they cannot be drawn 2.7 to 4.1 times at 35-50 C., and the desired resilient product is not obtained with lower draw ratios. While they can be drawn at higher temperatures, the initial modulus of the drawn product is then considerably higher than that of fine wool.

When as-spun polyethylene terephthalate filaments exhibit birefringence in the critical range from 0.004 to 0.011 the polymer molecules are not disstributed randomly, but in some regular manner. It is perhaps the beginning of orientation, although orientation does not show up in X-ray diagrams of the material.

The birefringence of the polyethylene terephthalate as-spun filaments is. dependent upon the polymer-intrinsic viscosity, the spinning speed and the rate of cooling of the freshly spun filaments. All other conditions being equal, an increase in the polymer intrinsic viscosity results.in a corresponding increase in the birefringence exhibited by the filaments. The birefringence also increases with spinning speed as measured at the take-up and with more rapid cooling of the filaments as they leave the spinneret. This is illustrated to some extent in Example 4, where the heavier denier filaments, which do not cool as fast as the finer denier filaments, exhibits a lower birefringence.

The polyethylene terephthalate multi-filament yarn used in the process of this invention for the preparation of textile denier filament yarn and staple is readilyprepared by spinning 0.50 to 0.70 intrinsic viscosity polymer at speeds in the range of about 900 to 1800 yards per minute. Of course, higher viscosity polymer can be used at lower spinning speeds, but such a process is not as economical. On the other hand, lower intrinsic viscosity polymers can be spun at higher speeds to obtain the proper birefringence. However, the spinning of the lower molecular weight polymers is more difiicult and .the tensile properties of the yarn are not so good as those of the higher intrinsic viscosity polymer yarn. Surprisingly, the polyethylene terephthalate yarn spun in the preferred manner differs from that described in the prior art, in that it can be stored indefinitely before drawing without becoming brittle and diflicult to process.

The yarn should be drawn to at least of its maxi- ..mum extensibility at 35 to 50 C., a draw ratio of nearly 4.1 times generally being obtained, although the ratio may be as low as 2.7 times with some yarns of the class described, particularly those whose birefringence is at or near 0.011. At temperatures below 35 C., the desired draw ratio is difiicult to obtain and the physical properties'of the final yarn are below the desired level. At temperatures much above 50 C., the maximum draw ratio rapidly increases and yarn drawn to 90%-100% of the maximum extensibility will not possess the resilient properties of fine wool. If the yarn is only partially .drawn to a draw ratio of 4 at temperatures above 50 C both denier and dyeing non-uniformity result.

The yarn should be wet thoroughly before passing over the draw rolls. Any hydroxylated non-solvent may be .used, such as water, ethylene glycol, glycerol, and the like. Water and dilute aqueous solutions containing a finish for the yarn are preferred. As illustrated in Example 1, it is quite convenient to apply the yarn finish at this point in the process. conventional means.

. The schematic apparatus shown in the accompanying The yarn may be wet by any drawing represents a convenient method for wetting and drawing the yarn. In this figure, the tray 13 contains wetting liquor heated to a temperature of around 40 C. The yarn 14 to be drawn is fed over rolls 1, 2, 3 and 4, passes through the liquid bath, and is then fed over rolls 5 through 12, respectively. Rolls 5, 6, 7 and 8 are 7 heated to the same temperature as thebath. The remainder of the rolls are not heated. Rolls 1 through 8 arerotated at the sameperipheral speed while rolls 9 through 12 have a peripheral speed of 2.7 to 4.1 times greater. Neglecting slippage on the rolls, a drawing of 2.7 to 4.1 times takes place between rolls 8 and 9.

The drawing process is applicable to single ends of yarn, to a plurality .of yarn ends in warp form, or to heavy denier tows. At the low temperatures involved, heating the yarn uniformly is no problem. Equipment can, therefore, be simple and operational difficulties minivrnized.

While the fibers and yarn prepared in accordance with this invention are capable of some spontaneous crimping when relaxed, as by being heated to an elevated temperature under little or no tension, it is preferred to crimp them mechanically. This can be accomplished conveniently by passing a tow comprising several ends of yarn through a stuffing box type crimper. The crimping operation is not essential in providing the final yarn with the resilience properties of fine wool, but it aids in subsequent'mill processing. If the yarn is to be mechanically crimped, this operation is performed preferably after drawing and before relaxation.

Theyarn finally acquires the resilience properties of fine wool during relaxation and setting. The yarns are relaxed and set by heating them to temperatures in the range of 90 to 200 C. under little or no tension. Suitable heating media include hot air, hot or boiling water, saturated or super-heated steam and various hot solutions th'atexert a mild plasticizing action on the material, for example, dilute nitric acid. At the higher temperatures,

for example, around 150 C., the treatment may be for short periods of time, such as two minutes. Treatment 'at the lower temperatures should generally be for longer periods of time ranging up to 15 minutes or more, although exposure of the fibers to a shower of water at 90 -l00 C. for a few seconds has been used successfully. This heat treatment stabilizes the yarn and increasesthe degree of crystallization, and also reduces residual shrinkage at the same time. If desired, the fibers may be for- -warded directly from the drawing operation, or after crimping, through a suitable bath or heated chambers before being wound up or cut into staple.

Prior to this invention, textile-denier filaments of polyethylene terephthalate could not be drawn at temperatures below 60 C. without excessive breakage, even when wet.

Theas-spun yarn was 'known to become brittle on standing, and subsequent drawing of the brittle yarn-was diificult evenat'temperatures above 60 C. The discovery that filaments of polyethylene terephthalate having a birefringence of 0.004 to 0.011 can be drawn wet at temperatures below 60 C. is essential to this process for preparing a synthetic fiber possessing the desirable characteristics of fine wool. Since these filaments do not become brittle on standing, an added advantage is that the as spun yarn does not have to be drawn soon after spinning.

An'outstanding feature of this invention is the production of a uniformly drawn product. The process provides for a means of obtaining a low draw ratio while drawing the yarn to at least 90% of its maximum extensibility. That good denier uniformityis obtained is con- .firm'ed by the uniformity of subsequently dyed fabrics. Another important advantage obtained from drawing the fabric may be produced from them which is crisp and firm to the touch and, nevertheless, feels soft and compliant when severely crushed in the hand. These fibers and yarns of'polyethylene terephthalate materials possess, in addition, much greater strength and wearresistance thanwool fibers and arenot attacked by moths,

Fabrics made from these fibers are extremely lively and wrinkle resistant, with desirable drape and; excellent crease retentivity. They are remarkably insensitive to water and changes in humidity. Also of importance is the versatility which the fibers possess over and above that of wool for processing into fabrics. They are useful, particularly in staple form, in felts of variou's'kinds, including paper-makers felts, carpets, mens and womens suits, bathing suits, sweaters, knitting yarns, as the wai'p in Turkish towels and the like.

Suiting fabrics prepared from the staple fibers produced in accordance with this invention are particularly outstanding. These are equal to' or better than high grade woolen suiting fabrics in wrinkle resistance, :recovery from wrinkling, and retention of ironed creases. Trousers may be cleaned by washing in an'automatic washer and hanging them up todry; they do not shrink appreciably, retain their original creases, and need 'no further pressing. Y

Since many different embodiments ofthe'inVention may be made without departing from the spirit and'scope thereof, it is to be understood that the invention'isnot limited by the specific illustration except to the extent defined in the following claims.

What is claimed is:

1. In the process for wet-drawingpolyethylene terephthalate 'fibers'to-obtain strong, "molecularly oriented textile fibers the improvement for producing uniform artificial fibers having the resilience characteristics of the better grades of wool which comprises drawing while wet with inert aqueous medium at temperatures in the range of 35 to 50 C. polyethylene terephthalate fibers of textile denier, having a birefringencein the rangelio f 0.004 to 0.011 and a corresponding maximum draw ratio 'of 4.1 to 2.7 at 35 to 50 C., to at least of said maximum draw-ratio and heating the drawn fibers in a free-to-shrink condition at temperatu'res'in the rangeof 90 to 200 C. until relaxed and set.

2. A process for producing uniform artificial fibers having'the resilience characteristics of thebetter grades of wool which comprises wetting with water polyethylene terephthalate fibers of textile denier having a birefringence in the range of 0.004 to 0.011 and a corresponding maximum draw ratio of 4.1- to 2.7 at 35 -to'50? 'C., drawing the wet fibers at temperatures in the range of 35 to50 C. to at least 90% of said maximu'm'j' draw ratio, and heating'the drawn fibers in a'free-to-shrink condition at temperatures in the rangeof 90 to 200 C. until wool-like fibers are produced and relaxed and set.

3. A' process for producing uniform :artificial fibers havingthe resilience characteristics of thebetter grades of wool which comprises continuously passing polyethylene terephthalate yarn composed of textile=denier fibers having a birefringence in the range of 0.004 to 0.011

through'an aqueous bath which is both non-reactive with and anon-solvent for said-fibers, continuously'withdrawing the'wet yarn from the bath, passing theyarn over heated rolls until the wet yarn is at a'temperature of 35" to 50 C., continuously drawing thewet'yarn at 35 to 50 C. to a maximum draw ratio of 2.7 to 4.1 times, and continuously passing the drawn yarn through a heating medium at 90 to 200 C. in a free-to-shrink condition until the yarn is relaxed and set and characterizedby an initial tensile modulus in the range of to 550 .kg./ mm. a complianceratio in the range of.0.05 to 0.17, and a tensile recoveryof atleast 55% from extension of 3%.

4. A process for producing uniform artificial fibers having the resilience characteristics of the better-:g'rades of wool which comprises preparing polyethylene .terephthalate fibers ofxtextile denierexhibiting' birefringence in the range of 0.004 to 0.011 by spinning 0.50 to 0.70 intrinsic viscosity polymer at speeds in the range of about 900 to 1800 yards per minute, wetting the fibers with water, drawing the wet fibers at temperatures in the range of 35 to 50 C. to a maximum draw ratio of 2.7 to 4.1 times, and heating the drawn fibers in a free-toshrink condition at temperatures in the range of 90 to 200 C. until relaxed and set and characterized by woollike resilience.

5. A process for producing fibers having the property of relaxing to form uniform fibers having the resilience characteristics of the better grades of wool when heated in a free-to-shrink condition at temperatures in the range of 90 to 200 C. until set which comprises wetting with 5 times.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,199,411 Lewis May 7, 1940 2,249,756 Finzel July 22, 1941 2,285,522 Alfthan June 9, 1942 FOREIGN PATENTS 603,840 Great Britain June 23, 1948 

4. A PROCESS FOR PRODUCING UNIFORM ARTIFICIAL FIBERS HAVING THE RESILIENCE CHARACTERISTICS OF THE BETTER GRADES OF WOOL WHICH COMPRISES PREPARING POLYETHYLENE TEREPHTHALATE FIBERS OF TEXTILE DENIER EXHIBITING BIREFRINGENCE IN THE RANGE OF 0.004 TO 0.011 BY SPINNING 0.50 TO 0.70 INTRINSIC VISXOSITY POLYMER AT SPEEDS IN THE RANGE OF ABOUT 900 TO 1800 YARDS PER MINUTE, WETTING THE FIBERS WITH WATER, DRAWING THE WET FIBERS AT TEMPERATURES IN THE RANGE OF 35* TO 50 *C. TO A MAXIMUM DRAW RATIO OF 2.7 TO 4.1 TIMES, AND HEATING THE DRAWN FIBERS IN A FREE-TOSHRINK CONDITION AT TEMPERATURES IN THE RANGE OF 90* TO 200* C. UNTIL RELAXED AND SET AND CHARACTERIZED BY WOOLLIKE RESILIENCE. 